A spark plug for use in an internal combustion engine, such as an automobile engine, includes, for example, a center electrode extending in an axial direction, an insulator provided outside the center electrode, a cylindrical metal shell provided outside the insulator, and a ground electrode having a base end joined to a leading end of the metal shell. The ground electrode is arranged in a bent manner such that a distal end of an inner periphery thereof opposes the leading end of the center electrode, whereby a spark discharge gap is formed between the leading end of the center electrode and the distal end of the ground electrode. In addition, there is proposed a technique for enhancing spark wear resistance by joining a tip (a noble metal tip) made of a noble metal alloy to the leading end of the center electrode and the distal end of the ground electrode, respectively (see Patent Document 1, for example).
From the viewpoint of fulfillment of superior performance for a heat radiation of the ground electrode, there is a known technique providing the ground electrode having a two-layer structure including an outer layer made of a Ni alloy and an inner layer made of a copper alloy that is metal superior to the Ni alloy in terms of heat conduction, and the like.
Patent Document 1: JP-A-5-242952